In the production of hollow cast components, for example turbine components, the production of the cavity is of particular importance. For example, turbine blades for gas turbines comprise a blade surface, which has a leading edge and a trailing edge. The leading and trailing edges are connected together by a wall on the suction side and a wall on the pressure side. Between the walls on the suction and pressure sides, at least one cavity is arranged which extends through a major part of the blade surface and is used to supply a coolant, for example air or steam, by which the turbine blade is cooled during operation of the turbine. The cooling effect depends on the configuration of the cavity and its accurate positioning inside the blade surface. Comparatively minor deviations in the positioning of the cavity can lead to a considerable difference in the cooling effect.
The shape and position of the cavity inside the blade surface therefore represent a challenge for the design of turbine blades. Not infrequently, a range of design modifications are required in order to optimize the placement and shape of the cavity in relation to the outer contour of the turbine blade, until the final design is established. In the development process, turbine blades with different designs are produced and tested, before the final design is established.
The production of hollow cast turbine blades for gas turbines, for example, is carried out by means of a ceramic precision casting technique. During this, a core made of a ceramic material is injected or cast in order to define the cavity. This core is subsequently placed into a mold for injecting or casting a wax pattern, and the wax is injected or cast into the mold. After the wax has cooled, the finished wax pattern together with the ceramic core form a pattern for the precision-cast preparation of the turbine blade, which in the further course of the method is employed to produce a ceramic mold for casting the turbine blade. In order to produce the ceramic mold, a ceramic shell is applied around the wax pattern. After the ceramic shell has been cured, the wax of the wax pattern is melted out so as to leave a mold for casting the hollow turbine blade. This mold comprises on the one hand the ceramic shell and on the other hand the ceramic core. Such a method is disclosed, for example, in U.S. Pat. No. 5,465,780.
Since, despite numerical aids for the simulation of flow and cooling properties, corrections of the core design have to be carried out by means of tests in the final stage of the product development, the described method of product development is relatively expensive because new casting or injection molds for the core and the wax pattern need to be produced for each design.
DE 101 29 975 A1 has therefore proposed to equip the casting or injection molds for casting the core with replaceable inserts, so that the core design can be modified without having to produce completely new casting or injection molds for the core. This procedure, however, merely allows local corrections but not overall correction of the core design. Furthermore, in the method described in DE 101 29 975 A1, corrections to the design of the outer contour of the turbine blade are not possible without producing new tools for this, for instance new casting molds.
The production of tools for manufacturing the ceramic cores and the wax patterns is elaborate and cost-intensive, as before. For example, large parts of the development time and the development costs during the production process development for hollow cast turbine blades are spent on production of the tools. Furthermore, the tools cannot be released for mass production until after the design of the hollow cast turbine component has been approved. Otherwise, modifications to the design could lead to a considerable time delay and high costs.
DE 32 11 777 A1 discloses a method for producing a metal turbine blade from two blade halves, which are metallurgically connected together.
GB 2 096 525 A likewise discloses that two metal turbine blade halves are connected together.